"Google will announce if we intend to discontinue or make backwards incompatible changes to this API or Service. We will use commercially reasonable efforts to continue to operate that Service without these changes until the later of: (i) one year after the announcement or (ii) April 20, 2015"
"Unless otherwise noted by Google, material changes to the Agreement will become effective 90 days after they are posted, except if the changes apply to new functionality in which case they will be effective immediately. If Customer does not agree to the revised Agreement, please stop using the Service."
"Google will announce if we intend to discontinue or make backwards incompatible changes to this API or Service. We will use commercially reasonable efforts to continue to operate that Service without these changes until the later of: (i) one year after the announcement or (ii) April 20, 2015"
So you have a year, at a minimum.